The Documentation Number
This has to be done, but isn't on many documented boats. The way I did it is I had a copper plate made with the No. ####### on it, and then epoxied and bolted the plate to the interior of my boat. According to the VSC I had done last week, it's fine.
The name and hailing port
From everything I've seen, non-commercial vessels can have the name of the boat on the port and starboard side of the boat, and the hailing port on the stern. That is how many sailboats I've seen are marked. The name of my boat is in letters over 10" tall. The home port, which is fairly long, is in letters as tall as possible, but not quite 4" high.
If you're looking for regular lettering, rather than custom lettering, you can find 4" numbers and letters at Home Depot or most home improvement stores, for use on mailboxes and the such. They're adhesive vinyl, and should work on a boat just fine.
BTW, Donna Lange's boat, Inspired Insanity
, which is homeported in the US Virgin Islands
has the name across the stern, and if seen from the side, it says "Inspired Virgin"
and "Insanity Islands"
BTW, most sign companies in your local area can make up a set of vinyl letters for your boat name and homeport in various colors and fonts. Well worth checking out.